1. Field of the Invention
This invention relates generally to a new and improved system for sampling and analysis of body fluids and the like, and may also include delivery of therapeutic agents in response to such analysis. More particularly, the invention relates to new and improved methods and apparatus for non-invasively withdrawing analytes from a biological subject automatically and controlling subsequent administration of therapeutic agents.
2. Description of the Related Art
Diagnosis for many human ills is dependent on evaluation of invasive samples of body fluids taken for assay. This invasive procedure is accomplished by withdrawal of the analyte or sample through a needle or the like, with consequent exposure of the patient to injury, possible infection and discomfort. The procedure invariably involves medical professionals that add to the cost of the procedure, e.g. an office visit.
Advances have recently been made in the biosensor field that enable diabetics, for instance, to self-test through the convenience of kits such as the ExacTech.RTM. device disclosed in U.S. Pat. Nos. 4,545,382 & 4,711,245. Such a device, while performing a valuable service and representing a quantum leap over professional intervention, is however, still invasive and subjects the patient to the same risks through multiple pin pricks and the like.
One approach to overcoming the aforementioned major shortcomings of invasive procedures is by noninvasive electro-osmotic analyte withdrawal through the unbroken skin or mucosal membrane. Electro-osmosis, sometimes referred to as cataphoresis and/or reverse iontophoresis, was recognized before 1941 by Nernst who showed that urea and sugar can be electrically transported out of the unbroken skin. An extensive bibliography exists on this basic phenomena.
A recent effort by Guy, et al., e.g. as described in U.S. Pat. Nos. 5,279,543 and 5,362,307, attempts to use this basic electro-osmosis technology to extract glucose. However, these attempts fall short of practical success because the proposed technology cannot perform the desired withdrawal procedure within a time span of less than ten minutes, as medically needed so that a glucose measurement would be followed in a timely manner after determination of the appropriate therapeutic insulin level. In this regard, continuously rapid changes of glucose levels, which commonly occurs, require different therapeutic insulin levels. Such limiting constraints on faster performance of sample withdrawal by the prior art is due to the restricted levels of current, voltage and time duration for the device to extract a sample and yet prevent skin injury. Accordingly, the prior art systems offer nothing new in basic electro-osmosis technology to prevent skin injury. Moreover, there is no subsequent controlled automatic delivery of an appropriate therapeutic agent in response to such rapid sample withdrawal and analysis.
Further difficulties have been encountered in achieving satisfactory dosimetry control for iontophoretic administration systems.
Hence, those concerned with the development and use of analyte withdrawal and evaluation systems have long recognized the need for very rapid, painless, accurate, non-invasive analyte withdrawal and analysis and subsequent controlled automatic delivery of therapeutic agents in response to such analysis. The present invention clearly fulfills all these needs.